A device for separating single flat articles from a lying stack is known, for example, from the publication U.S. Pat. No. 6,494,310. This device comprises a rotating suction wheel arranged at the front end of the stack support, on which the flat articles are standing.
The circumferential surface of the suction wheel moves upwards (parallel to the main surfaces of the stacked articles) immediately in front of the front end of the stack. The one article constituting the front end of the stack is pushed against the circumferential surface of the suction wheel by the stack feeding system and adheres to the suction wheel by the suction effect, to be lifted off the stack support while sliding relative to the following article. The suction effect on the circumference of the suction wheel is controlled in such a manner, that a following article is only adhered to the wheel and lifted, when the preceding article has already reached a position above the stack. Corresponding measures ensure, that the articles at the front end of the stack are not pressed against one another too strongly in order to prevent high pressure in the stack and therefore high friction between the stacked articles, which may lead to separation of not single articles but of pluralities of articles. This, however, is not desirable as it destabilises the front end of the stack.
In order to keep friction between articles low in the region of the front end of the stack, it is suggested in U.S. Pat. No. 6,494,310 that the article group forming the front end of the stack is isolated regarding pressing force from a rear stack region and that this group of articles is moved towards the front end as a relatively loose stack portion on a slightly downwards sloping and vibrating stack support. By this measure it is ensured, that forces acting in the area of the front end of the stack and pressing the articles against one another and towards the front end remain small and that therefore friction between these articles remains low. This measure enables reliable separation of one article after another with a very simple device.
The device in accordance with U.S. Pat. No. 6,494,310, however, is suitable only for handling relatively stable articles, i.e. articles which are capable of standing upright on one edge in a very loose stack, wherein the stack has to be the looser, the greater the friction coefficient between the articles is. The device further necessitates a mechanical stability of the articles such that they can be accelerated almost instantaneously by the suction wheel, whose circumferential surface moves with a constant speed in a direction essentially perpendicular to the stack support. Sensitive articles may suffer undesirable deformation or even damage, in particular if, for a high separation capacity the rotation speed of the suction wheel is chosen to be high. Furthermore, the suction wheel or control of the suction cycle is to be adapted to the height of the articles above the stack support and if so required also to their width. This means that the suction wheel may have to be physically adapted for the processing of different article formats.